With increased worry about flooding, seismic activity, and other potential forces acting on a home, housing codes are calling for more shear walls. But what are they?

Many years ago, not long after the implementation of a brand new Florida Building Code, I designed and built a room addition for a lakefront home. Obviously, one of the design criteria was that we take full advantage of the waterfront views, so we needed a wall of windows that wrapped around a corner of the building. The total length of wall space made mostly of glass was around 25 feet. I thought the end result was going to look great, but the structural engineer on the project saw a problem. "Not enough shear wall." he said, flatly. "You've gotta lose some of these windows."

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I knew that losing the windows wasn't an option, even if it meant building remaining structure out of solid steel and concrete. That was the solution, but I still had to ramp-up my understanding of what a shear wall does to defend the viability of my design.

Essentially, the term "shear wall" refers to a segment of wall that is strengthened by using more or stronger materials, more fasteners, additional bracing, and fewer openings. These sections of wall are meant to do double duty. First, they usually do the same thing as all other load-bearing walls, which is to hold the roof up (and down in the event of high wind uplift). But they also serve the purpose of holding the building up against sideways (lateral) forces. High winds against an exterior facade, seismic forces pushing a building from side-to-side, and even the onslaught of floodwaters from a storm surge or river flooding all push sideways on a building. Shear walls are designed to stand up against those forces.

As building codes everywhere are revised to include provisions for high winds, floods, and seismic activities, this type of engineering requirement is increasingly common. Now, when you tell your architect or contractor you must have that wall of glass and they tell you it can't be done, at least you'll know what you're up against.

Tim Layton is a home and DIY blogger for Popular Mechanics. Follow him on Twitter: @RemodelingGuy